The mesh instance's position in the render component's meshInstances array.
The runtime name of the mesh instance's current material, reported as-is: the engine
names an unnamed glTF material Untitled, and assigns a shared material named
defaultGlbMaterial to a primitive authored without one — neither is a unique authored
identifier. null when a script has cleared the assignment.
One material assignment of a HierarchyNode with a render component: a mesh instance's position within the component and the runtime name of its current material.